The goal of this project is to continue to make available to qualified investigators appropriately purified and assayed erythropoietin preparations. A wide variety of such preparations will be required since the research uses contemplated include the following: Clinical tests of erythropoietin and preparatory suitable animal experimentation, development of a radioimmuno assay of erythropoietin, study of the biochemical nature - cellular site of action - mechanisms of action of human erythropoietin - development of new purification procedures and assay methods. A laboratory shall be maintained to receive crude preparations of human erythropoietin from the urine of anemic individuals as collected from various populations. This material will be refined and fractionated by biochemical procedures established in this laboratory. New procedures will be developed. Materials will be carefully assayed both in vivo and in vitro. Stocks will be kept on inventory and dispensed to qualified investigators according to the directions of an appropriate N.I.H. committee. As part of this proposal, the biochemical characterization and the study of the mechanisms of action of erythropoietin by in vitro technique continued.